Open collector / open drain integrated bidirectional digital isolator

ABSTRACT

An open collector/open drain interface, such as I 2 C interface between two or more integrated circuit devices, employs isolation techniques to provide electrical isolation of a digital signal for transmission of the signal between the devices. Uni-directional isolator channels are utilized to transmit bidirectional digital signals, and a selection of an isolator channel operating in an intended transmission direction is performed by direction control logic. Edge detection logic is utilized to determine changes in edges of a digital signal, thus determining a transmitting device and a transmission direction. The direction state is held in a direction state register. This state is held until the appropriate edge is detected on the transmit side, returning the isolator to the idle state. In the idle state neither side of the isolator is in a driven state. During transmission, the digital signal is transmitted through an isolator channel and sent to a receiving device.

BACKGROUND

Isolation of digital signals communicated between devices is needed to reduce safety hazards as well as for noise robustness factors. Shock and fire hazards may result from digital signals that are not isolated. Additionally, excess noise may be introduced into the digital signals as a result of insufficient isolation. Thus, electrical isolation of digital signals being transmitted between devices, while still allowing the digital signal to be transmitted across an interface between the devices, is a necessary requirement.

Interface components, operating to communicate digital signals between devices, may be utilized to isolate the digital signals. Isolator channels are components for electrically isolating digital signals and may be employed in interface components for such a purpose. Isolator channels are uni-directional components, while digital signals may be bi-directional. Thus, one isolator channel may be utilized to transmit a digital signal in one direction, while a second isolator channel is needed to transmit the digital signal in an opposite direction. For example, the first isolator channel may be used for communication from a transmitter to a receiver, while the second isolator channel may be used for communication from the receiver to the transmitter.

When a digital signal reaches an interface between devices, it is necessary to determine the intended direction of the signal to allow for an isolator channel operating in the intended direction to be utilized to electrically isolate the digital signal. Thus, a need exists for a process and component to manage and control the direction of the signal across the interface.

SUMMARY

An open collector/open drain digital signal, such as, an I²C signal is communicated between two or more devices, such as microprocessors or peripheral devices, across an interface. The interface operates to receive, isolate, and transmit the digital signal. Isolator channels or isolation techniques are employed at the interface to electrically isolate the devices while still allowing the transmission of the digital signal. The isolator channels or isolation techniques are managed by direction control logic, that controls the direction of the signal across the interface. The direction control logic may employ edge detection techniques, operating to determine a transmitting device, isolate the signal in the direction towards the receiving device, and transmit the signal to the receiving device.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary and the following detailed description are better understood when read in conjunction with the appended drawings. Exemplary embodiments are shown in the drawings; however, it is understood that the embodiments are not limited to the specific methods and instrumentalities depicted herein. In the drawings:

FIG. 1 is a diagram illustrating an exemplary open collector/open drain interface component for isolating bidirectional digital signals;

FIG. 2 is a diagram illustrating exemplary direction control logic; and

FIG. 3 is a flowchart illustrating an exemplary method of communicating a digital signal across an interface.

DETAILED DESCRIPTION

With reference to FIG. 1, a diagram illustrating an exemplary open collector/open drain interface component 100 for isolating bi-directional digital signals is shown. The interface component 100 may be used as an I²C interface, for example. The interface component 100 may also be utilized as an interface between a microprocessor and a peripheral chip, between two master peripheral chips, or between any components used for exchange of digital data.

The interface component 100 may operate to communicate and electrically isolate a digital signal between two devices, such as device 140 a and device 140 b. Bi-directional communication ports 110 a and 110 b may act as the link between the devices 140 a and 140 b and the interface component 100. The bi-directional communication ports 110 a and 110 b may operate to transmit and receive the digital signal between the two devices 140 a and 140 b. The digital signal may be a serial clock signal or a serial data signal, for example. Other types of digital signals may be communicated between the devices 140 a and 140 b across the interface component 100. Moreover, the interface component 100 may include additional bi-directional communication ports. Two ports, 110 a and 110 b, are shown only as an exemplary embodiment, as illustrated in FIG. 1.

Isolator channels 130 a and 130 b may be uni-directional isolator channels that operate to provide high-volt electrical isolation to digital signals. The means of isolation may be, but are not limited to, capacitive, magnetic, optical, or acoustical means.

Direction control logic 120 may be used to determine a direction of the digital signal. The digital signal may be a bi-directional digital signal. Upon determination of the direction of the digital signal, direction control logic 120 may provide the digital signal to one of two isolator channels 130 a or 130 b operating in the determined transmission direction. Transmit drivers 138 a and 138 b may then allow the transmission of the digital signal to the respective device 140 b and 140 a.

For example, the digital signal may be transmitted from a first device (140 a) to be received by a second device (140 b), or the second device (140 b) may transmit the digital signal to be received by the first device (140 a). The direction control logic 120 may determine the intended transmission direction of the digital signal by detecting an edge change in the digital signal. A default state of the edge of the digital signal may be high. The direction control logic 120 may monitor the digital signal and detect a change in the edge of the digital signal from high to low, thus detecting a desired transmission direction. Alternately, the default state of the edge of the digital signal may be a low state. In this case, the direction control logic 120 may, while monitoring the digital signal, detect a desired transmission direction when the edge of the digital signal changes from low to high.

The direction control logic 120 determines from which device, 140 a or 140 b, the desired transmission is initiated and allows the transmission of the digital signal through the isolator channel, 130 a or 130 b, operating in the intended transmission direction. Isolator channel 130 a may operate to isolate and transmit digital signals from device 140 a to device 140 b; while isolator channel 130 b may isolate and transmit digital signals from device 140 b to device 140 a. For example, direction control logic 120 may detect a change from high to low in a digital signal from device 140 b. Upon this determination, direction control logic 120 transmits the digital signal through isolator channel 130 b to be isolated and transmitted to device 140 a. FIG. 2 is a diagram illustrating details of the exemplary direction control logic 120 of the interface component 100. Synchronization logic 122 may include synchronization flip-flops to synchronize the asynchronous digital signals coming into the isolator. Edge detection logic 124 may detect the edge change in the digital signal and may thus determine the intended transmission direction of the digital signal. The direction state register 126 may hold the direction state until the transmitting side returns to the high state. The transmit disable gates 129 a and 129 b prevent the receiving side from transmitting a low state back around to the transmitting side and causing the isolator to be stuck in a self reinforcing low-state on both sides.

FIG. 3 is a flowchart illustrating an exemplary method of communicating a digital signal across the interface component 100 positioned between devices 140 a and 140 b. The interface component 100 may operate to electrically isolate a digital signal, which may be a bi-directional signal, between devices 140 a and 140 b.

At 305, the digital signal is received from one of device 140 a or 140 b, operating as the transmitting device. The digital signal may be received by an exemplary open collector/open drain interface component 100 from a bi-directional communication port 110 a or 110 b.

At 310, the edge of the digital signal is monitored. The edge may be monitored on a bit-by-bit basis. Other rates may be used for the monitoring operation. The edge may be monitored to detect a transmission of the digital signal. At 315, a fall in the edge of the digital signal from a high state to a low state is detected. The monitoring and edge-change detection may be performed by direction control logic 120, operating to determine an intended direction of the digital signal.

At 320, the direction in which to transmit the digital signal is set. The intended direction of the digital signal may be determined by detecting the device, 140 a or 140 b, transmitting a low state. The transmitting device may be determined by detecting from which device, 140 a or 140 b, the digital signal changes from a high to low state. The change in edge of the digital signal signifies an intended transmission of the digital signal.

At 325 the appropriate transmit disable gate, 129 a or 129 b, disables transmission of a logic low state from the receiving side to the transmitting side. This is done to prevent the open collector/open drain interface component 100 from getting into a dead lock state in which a self reinforcing low state is held at both sides of the interface component 100.

At 330, the digital signal is transmitted over an isolator channel. The transmission of the digital signal over an isolator channel provides high voltage electrical isolation between the transmitting device (140 a or 140 b) and the receiving device (140 a or 140 b). The transmission of the digital signal over an isolator channel may include utilizing a uni-directional channel to isolate the digital signal between the two devices, 140 a and 140 b. The uni-directional channel may be an isolator channel 130 a or 130 b.

At 335, the digital signal is transmitted to the receiving device. The digital signal may be transmitted to the correct device 140 a or 140 b over a bi-directional communication port 110 a or 110 b, depending on which device, 140 a or 140 b, receives the digital signal.

At 340, a rising edge of the digital signal is detected at the transmitting side, indicating that transmission of the digital signal is complete. At 345, after transmission of a low state, the direction control logic 120 may be reset to the idle state upon the return to the high state at the transmitting side. In the idle state, neither side of the isolator is in a driven state.

The foregoing examples are provided merely for the purpose of explanation and are in no way to be construed as limiting. While reference to various embodiments are shown, the words used herein are words of description and illustration, rather than words of limitation. Further, although reference to particular means, materials, and embodiments are shown, there is no limitation to the particulars disclosed herein. Rather, the embodiments extend to all functionally equivalent structures, methods, and uses, such as are within the scope of the appended claims. 

1. A method of communicating a digital signal across an interface, wherein the interface is positioned between two devices, a transmitting device and a receiving device, and wherein the interface operates to isolate, receive, and transmit bidirectional digital signals between each of the two devices, the method comprising: receiving the digital signal from the transmitting device; detecting a change in the edge of the digital signal from a high state to a low state; determining a direction to transmit the digital signal; transmitting the digital signal over an isolator channel, operating in the determined direction, to isolate the digital signal; and transmitting the digital signal to the receiving device.
 2. The method of claim 1, further comprising: monitoring the edge of the digital signal.
 3. The method of claim 2, wherein monitoring the edge of the digital signal comprises monitoring the edge of the digital signal on a bit-by-bit basis.
 4. The method of claim 1, wherein transmitting the digital signal over an isolator channel provides high voltage electrical isolation between the transmitting device and the receiving device.
 5. The method of claim 1, wherein transmitting the digital signal over an isolator channel comprises utilizing a uni-directional isolation channel operating to electrically isolate digital signals between the transmitting device and the receiving device.
 6. The method of claim 1, further comprising: upon transmission of the digital signal to the receiving device, regulating the isolator channel to prevent transmission of a second digital signal from the transmitting device to the receiving device.
 7. The method of claim 1, wherein receiving the digital signal from the transmitting device comprises receiving the digital signal from a bi-directional communication link; and wherein transmitting the digital signal to the receiving device comprises transmitting the digital signal over a bi-directional communication link.
 8. An interface component for communicating and electrically isolating a digital signal between two devices, the interface component comprising: bidirectional communication ports for transmitting and receiving the digital signal between the two devices; direction control logic for determining a direction of the digital signal between the two devices by detecting an edge change in the digital signal and for transmitting the digital signal in the determined direction; and unidirectional isolator channels for isolating the digital signal upon determination of the direction of the digital signal.
 9. The interface component of claim 8, wherein the direction control logic comprises: synchronization logic for synchronizing the digital signal; edge detection logic for detecting the edge change in the digital signal; and direction state register for holding the determined direction during a transmission of the digital signal
 10. The interface component of claim 8, further comprising: transmit disable gates for preventing transmission of a second digital signal from a receiving side to a transmitting side.
 11. The interface component of claim 8, wherein a first of the two devices is a microprocessor and a second of the two devices is a peripheral chip.
 12. The interface component of claim 8, wherein each of the two devices is a peripheral chip.
 13. The interface component of claim 8, wherein the isolated digital signal is transmitted to a receiving device through a bidirectional communication port connected to the receiving device.
 14. One or more integrated circuit device having a process embodied in said integrated circuit device, said process performing a method of isolating a digital signal across an interface, the method comprising: monitoring a digital signal received from a transmitting device; detecting a change in the edge of the digital signal from a default state; determining a direction to transmit the digital signal; isolating the digital signal; and transmitting the isolated digital signal to a receiving device.
 15. The one or more integrated circuit device of claim 14, wherein isolating the digital signal comprises transmitting the digital signal over an isolator channel, operating in the determined direction.
 16. The one or more integrated circuit device of claim 15, wherein said process performs the further method of: regulating the isolator channel to prevent transmission of a second digital signal from the transmitting device to the receiving device.
 17. The one or more integrated circuit device of claim 14, wherein detecting a change in the edge of the digital signal from a default state comprises detecting a change in the edge of the digital signal from a high state to a low state.
 18. The one or more integrated circuit device of claim 14, wherein said process performs the further method of: determining the receiving device based upon the determined transmission direction of the digital signal. 